In some internal combustion engines it may be desirable to vary the intake runner length, during operation, in order to optimize engine performance characteristics across a wide range. Runner variation may be achieved through the use of an intake manifold having two intake runners, of varying length, associated with each engine cylinder. The intake runners are valved into and out of communication with respective cylinders, based on engine parameters, using a valve system disposed between the runners and the engine. In such systems it would be desirable to avoid disruption of the inlet flow caused by turbulence in the inlet runners while minimizing the complexity of the valving system.
Port throttle valves typically used to regulate air flow to an internal combustion engine are "butterfly" valves composed of a body having a throat across which is a diametrically extending, rotatable shaft with a valve plate attached thereto. Butterfly valves are constructed from a multiplicity of parts which are, by design, difficult to assemble and calibrate. Clearances required for assembly of the many components assure that close tolerances are difficult to achieve and, as such, a fully sealing valve is unlikely.
It is known to use slide valves as an alternative to butterfly valves in intake systems for the control of intake air. Such slide valves have advantages over butterfly valves including a simplification of, and reduction in the number of parts required to assemble a valve, elimination of the flow disrupting center shaft in the air stream and greatly improved sealing characteristics of the valve member. Disadvantages of such valves have been in their propensity to stick or bind due to contaminant build-up, space requirements for the movement of the valve plate, and non-uniformity of flow through the valve under less than full flow conditions as a result of side-to-side valve movement.